Are counterflashings needed?

A study of SPF roof systems reveals how SPF flashings perform in the field

Every roof system needs a flashing system that works. Poor flashings have allowed water to get in and under the best of roof systems. Sometimes, water entry is attributable to an improper design detail; other times, it may be a problematic application. Often, flashing material fails because of the demands of direct weathering, differential movement, inadequate attachment, cumulative movement or other stresses. Spray polyurethane foam (SPF) roof systems are unique because of the direct use of SPF material as the flashing system.

For example, a roof mechanic applying SPF material literally applies SPF up a wall, curb or projection to a prepared elevation and stops. Flashing sheets and fasteners are not required. The use of metal as a counterflashing over SPF material and coating also may be used. Currently, The NRCA Roofing and Waterproofing Manual, Fifth Edition's construction details call for SPF roof systems to use metal counterflashings. This article addresses what is happening in the field with SPF flashing details that do not incorporate metal counterflashings.

Background

The use of SPF on roof systems began in the 1960s. But getting SPF recognized by the industry as a viable roofing material took some time. As a result, a number of independent studies of SPF roof systems had been conducted during the 1980s and early 1990s; papers about the studies can be found in the proceedings of the second and third International Symposiums on Roofing Technology (log on to shop.nrca.net to purchase the proceedings). And the Spray Polyurethane Foam Division, now known as the Spray Polyurethane Foam Alliance (SPFA), developed a contractor accreditation program that continues to publish technical bulletins about the design, use and installation of SPF roof systems.

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